This project will examine cognitive deficits in severe, life threatening anorexia nervosa before and after medical stabilization. Medical stabilization is established when the patient is consuming 2000-3000 kcal/day, the patient's laboratory values show that end organ failure is resolved or resolving, and that they are through the refeeding syndrome, the patient has minimal edema, and is physically strong enough to progress to eating disorder treatment programs, the patient is deemed as medically stable for discharge by the treating physician. The specific aims of this study are to quantify cognitive deficits in severe, lfe threatening anorexia nervosa, compare cognitive deficits before and after medical stabilization, compare cognitive deficits at baseline and medical stabilization between patients with the restricting subtype of anorexia nervosa to those with the binge-purge subtype, and to correlate changes in cognitive function to changes in serum leptin levels. Patients will be recruited from an acute medical stabilization unit that specializes in eating disorders. Patients will be between the ages of 18-35 and <70% ideal body weight. Patients will undergo cognitive testing within 3 days of admission and again at medical stabilization. Serum leptin levels will be measured at baseline and at medical stabilization. Changes in cognition will be correlated with changes in serum leptin levels.